Isotropic compression and triaxial shear characteristics of coral sand under high confining pressure and related particle breakage

It has been recognised that coral sand shares some common characteristics that all granular materials possess, but also exhibits some unique characteristics. This study utilised coral sand extracted from a reclaimed territory on a natural coral reef in the South China Sea (SCS) as the experimental material; a suite of tests including monotonic and cyclic triaxial shear (drained or undrained) and drained isotropic compression were performed at high confining pressure (3, 5, 10 MPa, respectively). The test results show that it is difficult for coral sand to reach the strictly defined critical state under high confining pressure. Under the drained condition, specimens constantly contracted and exhibited significant particle breakage. During the isotropic compression, the growth rate of plastic volumetric strain of coral sand visibly decreased as the confining pressure increased. Furthermore, there was a direct correlation between the elastic bulk modulus of coral sand and the level of confining pressure. The quantification analysis of coral sand particle breakage under high confining pressure was conducted, and the relationship between particle breakage and input plastic work was established. This study furnishes robust experimental evidence that is crucial for the subsequent formulation of a constitutive model for coral sand that incorporates considerations of particle breakage.